标题：A search for very high-energy flares from the microquasars GRS 1915+105, Circinus X-1, and V4641 Sgr using contemporaneous H.E.S.S. and RXTE observations
摘要：Context.Microquasars are potentialγ-ray emitters. Indications of transient episodes ofγ-ray emission were recently reported in at least two systems: Cyg X-1 and Cyg X-3. The identification of additionalγ-ray-emitting microquasars is required to better understand howγ-ray emission can be produced in these systems.Aim.Theoretical models have predicted very high-energy (VHE)γ-ray emission from microquasars during periods of transient outburst. Observations reported herein were undertaken with the objective of observing a broadband flaring event in theγ-ray and X-ray bands.Methods.Contemporaneous observations of three microquasars, GRS 1915+105, Circinus X-1, and V4641 Sgr, were obtained using the High Energy Spectroscopic System (H.E.S.S.) telescope array and theRossiX-ray Timing Explorer (RXTE) satellite. X-ray analyses for each microquasar were performed and VHEγ-ray upper limits from contemporaneous H.E.S.S. observations were derived.Results.No significantγ-ray signal has been detected in any of the three systems. The integralγ-ray photon flux at the observational epochs is constrained to beI(>560 GeV) < 7.3 × 10−13cm−2s−1,I(>560 GeV ) < 1.2 × 10−12cm−2s−1, andI(>240 GeV) < 4.5 × 10−12cm−2s−1for GRS 1915+105, Circinus X-1, and V4641 Sgr, respectively.Conclusions.Theγ-ray upper limits obtained using H.E.S.S. are examined in the context of previous Cherenkov telescope observations of microquasars. The effect of intrinsic absorption is modelled for each target and found to have negligible impact on the flux of escapingγ-rays. When combined with the X-ray behaviour observed using RXTE, the derived results indicate that if detectable VHEγ-ray emission from microquasars is commonplace, then it is likely to be highly transient.
